Process for fire-proofing cellulosic materials



Patented Aug; 27, 1935 unirao srA'rss FATE oFFicE PROCESS FORFIRE-PROOFING CELLULOSIC MATERIALS Martin Leatherman, Hyattsville, MIL,dedicated to the free use of the Public of the United States of AmericaNo Drawing. Application May 2,1934, Serial No. 723,546

3 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. {757) This application is in part a continuance of my applicationSerial Number 711,727, filed February 17, 1934.

This application is made under the act of March 3, 1883, as amended bythe act of April 30, 1928, and the invention herein described, ifpatented, may be manufactured and used by or for the Government forgovernmental purposes also largely prevents the outof-door deteriora- 4tion of cellulosic fabrics arising from the effects of certain generalclasses of treating materials,

when acted upon by sunlight.

It is well known that hydrated stannic oxide prevents flaming ofcellulosic materials when properly placed therein. However, it hasnever.

been established as to why or how stannic oxide inhibits flaming ofcellulosic fabrics when the said fabrics are exposed to an ignitingflame. I have discovered the mechanism involved in this said'flameproofing process and in order to make these specifications ascomplete as possible -I will briefly describe my discoveries and alsothe manner in which these discoveries were authenticated.

The three lines of investigation which I followed all tended to provethat stannic oxide flameproofs cellulose by setting up a catalyticdehydration of the cellulose under the influence of heat. In the firstplace, when untreated fabric samples and fiameproofed fabric sampleswere respectively heated in tubes at 325 C. in a stream of dry, CO2-free air, the exit gases obtained from the flameproofed fabric samplesinvariably showed much the larger percentage of C02. The samples in allcases were completely ashed before the air flow was stopped. The air andthe gases swept out with it were all collected in a large evacuatedbottle each time and aliquot samples of the collected gas were analyzedin a modified Orsat apparatus. The larger yield of CO2 from the treatedsamples indicated to me that with the treated, fiameproofed samples theproducts formed were largely CO2 and water, whereas with the'untreatedsamples the carbon was evolved as a constituent of volatile combustiblecompounds such as acetone; hydrocarbons, etc.

In the second phase of my investigations the carefully dried fabricsamples were heated in tubes in a stream of dried oxygen-free nitrogen,

the tubes being immersed in a molten metal bath at 325 C. for 240seconds. was filtered out of the exit gases and the evolved moisture wascollected and weighed. The percentage of water evolved, based on the netweight of the fabric, was always much greater in the case of the samplestreated with stannic .oxide.

The tarry matter The third-line of study was undertaken to eslo tablishbeyond any doubt that the stannic oxide effects its flameprooflng actionby splitting the cellulose into carbon and water; Treated and un-'treated samples were heated at 325 C. in tubes in a stream of driedoxygen-free nitrogen until most of the matter volatile at thattemperature was driven off, the heating being continued the same lengthof time in all cases. The container tubes were then connected with anabsorption train and the fabric residues were completely burned in astream of oxygen. In this way the carbon in the residues was determinedas carbon dioxide. Based on the net weight of carbon-in the,

original cellulose of the fabric samples, the percentage of carbon inthe residues from the de-.

' structive distillation of the treated fabric was nearly twice as great.as in the identically obtained residues from the untreated fabric.

Thus it was definitely proved that stannic oxide flameproofs celluloseby catalytically splitting the cellulose carbohydrate into carbon andwater and thereby preventing the formation of combustible gases. It nowbecame possible to improve the action of stannic oxide by applyingknowmprinciples of catalysis. In the first place, it has been shown byothers that alkali acts as a catalyst poison. Therefore, if it werepossible to precipitate stannic oxide in the cotton fabric under moreacid conditions a more pronounced fiameproofing effect should beproduced. The Perkin method Patent No. 856,906 of using fairly diluteammonium sulfate solutions to decompose the sodium stannate on thefabric precipitates the stannic oxide under alkaline conditions becauseof the ammonia evolved.

If, for example, instead of. using ammonium sulfate as the precipitantfor sodium stannate, ferric sulfate or chloride-is used, three effectsare obtained. In the first place a solution of ferric sulfate or offerric chloride is acid in reaction, as is ammonium sulfate, because ofhydrolysis.

The reaction between sodium stannate and the ferric salt, if an excessof the latter is used, leaves the solution from which the stannic oxideis deposited still acid, unlike ammonium sulfate, and

this lessens the quantity of alkali which can be absorbed by the freshlyprecipitated, gel-like stannic oxide. In the second place, ferric oxideis precipitated in intimate contact with the stannic oxide and therebyexerts catalytic promoter effects. Many other oxides exert similareffects. In the third place, and most important, the iron oxide colorsthe fabric and this coloring exerts a preservative action on the fabric.This is true of other colored oxides such as those of chromium,manganese, copper, cobalt, nickel; etc. Stannic oxide alone in fabricaccelerates deterioration of cotton fabric in sunlight.

The desirable catalytic action of stannic and other oxides inflameproofing of cellulose is accompanied by amost undesirable action.These oxides'are also catalysts for carbon combustion and after thedehydration mechanism liberates the carbon the oxide facilitates itscombustion. Consequently fiameproofed fabrics glow vigorously eventhough they do not flame. For this reason, to produce a fullyfirepro'ofed fabric, after flameproofing with metallic oxides, it isnecessary to use a supporting agent. From the standpoint ofweather-resistance there is only one type of material which willsufilce. type of material is represented by chlorinated organicsubstances of various kinds. It is known touse the chlorinated vinylresins in combination with tin oxide, but, while this treatmenteffectively fireproofs cotton, it is impracticable because both stannicoxide and chlorinated vinyl resin act very destructively on the fabricso that the fabric lasts only a short time. However,'1 have discoveredthat this destructive action is prevented by the presence of a coloringmaterial.

In the past, the chlorinated resinous materials have all beenobjectionable because of cost or undesirable physical or chemicalproperties. I have found that certain cheap petroleum derivatives can bechlorinated to give materials which are very well suited as glowproofingagents for use in connection with oxide mixtures in cellulose fabricsfor exposure to weather. The glowproofing effect results from theevolution of hydrogen chloride. at elevated temperatures. Thechlorinated product must not decompose spontaneously when properlyprotected, that is, by a coloring material, and it must evolve hydrogenchloride within a definite temperature range. I have discovered thathighly chlorinated paraflin wax answers these requirements but does nothave the desired physical properties, that is, it stiffens the fabrictoo much: If, before chlorination, I mix with the paraffin approximatelyits own weight of certain light bodied partially unsaturated liquidparafiin oils of low lubricating power,

such as are used by filling stations for flushing crank cases, I canintroduce a higher percentage of chlorine and still obtain a lessplastic product which does not unduly stifien the fabric but results ina flexible, soft, fire-proofed material which is also highly waterproofed. I prefer to have jin the finished chlorinated material fifty toseventy per cent of chlorine based on the total weight of product butthe percentage of chlorine may, within the spirit of my invention, beless or more than this.

' It is well known that tin is a rare metal and that its cost mustprogressively increase. One of the further merits of my invention liesin the fact that by using promoter oxides, a part of the tin necessaryfor flameproofing may be replaced with cheaper metal oxides. Anadditional merit of my invention lies in the possibility ofassisting,with- ThiS I out deleterious results,'the fiameproofing effect of theoxides by using the above-mentioned resinous chlorinated petroleumderivatives, which besides glowproofing the fabric, markedly assist in Atypical procedure which I may follow in producing a weather-resistantfireproofing treatment in cellulose fabrics is as follows: if the fabricis unbleached and water-resistant it is first soaked in a solution of awetting agent of either the sulphonated type or of the sulfate estertype for about five minutes, such as a one per cent aqueous solution ofametallic salt of a sulfate ester of an aliphatic alcohol, then squeezedout and rinsed thoroughly in water for about five minutes, after whichit is again squeezed out and immersed in sodium stannate solution forabout twenty minutes. When bleached and absorbent fabric is beingtreatedlthe wetting agent treatment is unnecessary. The sodium stannatesolution con-i .tains about twenty parts or less of alphasodium coloredprecipitate, as in the case of titanium or vanadium salts, it isnecessary to use a pre-' viously colored fabric or to introduce apigment later, preferably with the resin treatment. It may also bedesirable to mix enough ironor chromium salt with the titanium saltsolution to produce a colored precipitate in the fabric.

After the precipitation of the stannate, the

fabric is squeezed and immersed in aqueous or gaseous ammonia toprecipitate the balance of the iron or other metal which may have beenused. This additional amount of colored oxide obtained by the ammoniaprecipitation is of great value in that it gives a deeper color thanthat provided when the colored metallic salts are washed out, and thisdeeper color is very effective in further preserving the fabric againstdeteriora-' tion. When the ammonia precipitation is used,

less washing of the fabric is required, in fact,

where the sodium and amonium salts are not objectionable the fabric neednot be washed at all. However, ammonium salts tend to deteriorate thefabric in time and it will usually be desirable to wash them out. Afterdrying, the fabric is ready for the treatment with the glowproofingagent.

I have found that certain of the chlorinated diphenyls act as excellentplasticizers in connection with my chlorinated petroleum derivatives,and, in fact, in connection with other chlorinated resinous materials.The best chlorinated diphenyl derivative is one which exists as amoderately viscous liquid but I may use a chlorinated diphenylderivative which is less viscous or one which issolid. All of thederivatives obtained by chlorinating diphenyl are of value.

assist in preventing flaming in cellulosic materials butwhen used as Idescribe they appear to slightly assist the fiameand glow-proofingaction of the material which they serve to plasticize.

The percentage of chlorinated diphenyl to be required as a plasticizingmaterial will depend upon the physical properties of the said chlori-These materials by themselves do not materially nated diphenyl as wellas upon other factors. I

may use as little as fifteen parts of chlorinated diphenyl toeighty-five parts of chlorinated petroleum derivatives and I may useenough to equal the weight of the chlorinated petroleum derivativesemployed. I In general the total mixture impregnated into the fabricwill not exceed thirty per cent of the total weight of the treatedfabric, including precipitated oxides. For most purposes, twenty percent of the total weight of the finished fireproofed fabric will besuiiicient.

As a plasticizing agent there may be substituted in the place ofchlorinated diphenylsspecified charred portion of the fabric which hasbeen.

subjected to an igniting flame. Having made a full disclosure of thefunction of the glowprooflng and assisting agent I will now givespecific examples of compositions which are suitable for my purpose. 7

As a typical composition of the glowprooflng resin I may use 75 parts ofchlorinated petroleum products, preferably a chlorinated mixtureofparafiin wax and low-viscosity, partially unsaturated, petroleum oils,said chlorinated mixture to contain approximately sixty per cent ofchlorine based on total weight, and parts of chlorinated diphenyl. Formy purpose I will ordinarily use as a plasticizer a chlorinated diphenylwhich has a viscosity similar to that of heavy molasses. However, I donot restrict myself because I can use the chlorinated petroleumderivatives without any plasticizer at all or I can use chlorinateddiphenyls of a wide range'of physical properties mixed with thechlorinated petroleum derivatives in widely varying proportions.

In coating or impregnating the flame-proofed fabric with the chlorinatedresinous glowprooflng and assisting agent no definite solutionconcentrations can be specified because the proper and desiredconcentration will vary with the solvent employed, the pressure appliedin squeezingout excess solution and with the percentage which it isdesired to leave in the fabric. For a given concentration of solution, ahigh-volatile solvent like carbon tetrachloride will leave a higherpercentage of resin in the fabric than will low-volatile solvents suchas mineral spirit thinners. Also if the fabric is to be treated bydipping, the concentration will be different than if the resin solutionis applied by brushing.

The proportions of the respective ingredients present in the finishedflreproofed fabric may be varied considerably. For example, if thepercentage of flameprooflng oxides is increased, the

percentage of glowprooflng resin can be decreased to a certain point.Also the glowprooflng resin solution may be made the vehicle for apig--' ment, and a paint may thereby be prepared which is especiallyuseful in preparing striped awnings or in home treating of canvas onfarms or else- Fireproofed fabric denotes fabric whichwhere. As pigmentany earthy material such as ochre, sienna, umber, etc., or any coloredmetallic oxide may be used.

In the treatment as outlined in these specifications there is nowater-soluble constituent which can be leached out by rain and thepigmenting material stabilizes the chlorinated resinous constituent. Thefabric retains its fireproof characteristics and does not rapidlyloseits tensile strength as it will do when no pigment is present. Thepetroleum hydrocarbons furnish a cheap source of raw material forchlorination and the finished chlorinatedproduct is cheap enough to beused in low priced fabrics.

Having fully disclosed my invention, I claim:

cellulosic materials and fabrics which comprises immersing the fabricuntil thoroughly saturated in a one per cent aqueous solution of ametallic salt of a sulfate ester of an aliphatic alcohol, rinsing thecellulosic material thoroughly in water, pressing out as much of thewater as possible; then impregnating the cellulosic material with sodiumstannate, drying, and then immersing the dried cellulosic material in awater solution of a salt of a strong mineral acid with a weaklybase-forming metal, the hydroxide of which is water-insoluble, then withonly light squeezing immersing the wet cellulosic material in an ammoniasolution, then washing the mate-- rial in water to remove soluble salts,drying the 1. The process of fire-proofing and-preserving material,impregnating the material with a chlorinated mixture of paraffln wax andlowviscosity, partially unsaturated petroleum oil plasticized withchlorinated diphenyl derivatives and containing coloring materials.

2. The process of fire-proofing and preserving cellulose materials andfabrics which comprises immersing the fabric until thoroughly saturatedin a one per cent solution of a metallic salt of a sulfate ester of analiphatic alcohol, rinsing the cellulosic material thoroughly in water,pressing out as, much of the water as possible; then impregnating thecellulosic material with sodium stannate, drying, and then immersing thedried cellulosic material in an aqueous solution of ferric sulphate,then with light squeezing immersing the wet cellulosic material in anammonia solution, then washing the cellulosic material in water toremove soluble salts, drying the cellulosic material and impregnating itwith a chlorinated mixture of paraflin wax and lowviscosity, partiallyunsaturated petroleum oil containing chlorinated-diphenyl derivatives.

3. The process of fire-proofing and preserving cellulosic materials andfabrics which comprises immersing the fabric until thoroughly saturatedin a one per cent aqueous solution of a metallic salt of a sulfate esterof an aliphatic alcohol,

-rinsing the cellulosic material thoroughly in water, pressing out asmuch of the water as possible; then impregnating the cellulosic materialwith sodium stannate, drying, and then immersing the dried cellulosicmaterial in a water solution of a salt of a strong mineral acid with aweakly base-forming metal, the hydroxide of.

which is water-soluble and colored, then washing the material in waterto remove acid residues, drying the material and impregnating thematerial with a chlorinated mixture of paraflin wax and low-viscosity,partially unsaturated leum oil.

MARTIN LEATHERMAN.

pe o- CERTIFICATE or CORRECTION.

Patent No. 2,012,686. I August 21,1935.

MARTIN LEATHERMAN.

It is hereby certified that error appears in the printed specification.of, the

above numbered patent requiring correction as follows: Page 3, second,column,

line 67, claim 3, for "water-soluble" read water-insoluble; and that thesaid Letters) Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office.

Signed and sealed t?" 5th day of November, A. D. 1935,

Leslie Frazer (Seal) v ABt iIIICOmIHi'SSIOH BI of'Patents

